Field of the Invention
The present invention relates to a tire curing mold in which vent plugs are installed to exhaust holes on a molding surface coming into contact with an outer surface of a tire, and a manufacturing method for the tire using the same.
Description of the Related Art
In the tire curing mold, a lot of exhaust holes are provided on a molding surface which comes into contact with the outer surface of the tire, thereby discharging excess air between the tire and the molding surface to an external portion. As disclosed in patent document 1, there is a case that the vent plug is installed to the exhaust hole, whereby formation of a rubber projection called as spew can be reduced. Furthermore, as disclosed in patent documents 2 to 5, there has been known a vent plug (a spring vent) which is opened when a stem inserted to a tubular housing is urged by a spring and is closed when the stem is depressed by an outer surface of the tire.
In the spring vent, an uncured rubber flowing from a side direction flows into an inner portion from a gap between the housing and the stem before the stem is depressed. As a result, there has been a problem so-called rubber biting that the inflow rubber within the housing entwines the spring. In the case that the rubber biting is generated, the inflow rubber is not removed when the tire which is finished its cure is removed from the mold, and the inflow rubber remaining in the housing prevents movement of the spring. As a result, an operation defect of the vent plug is caused. Thus, there has been strongly desired to propose a method which can suppress generation of the rubber-biting.
In the patent document 2, there is described a vent plug (a spring vent) in which a top surface of a steal is formed by a protruding surface, and a top surface of the stem in a closed state is arranged at a position which sinks a little from a molding surface. However, since a projection having a top surface which is formed by a recessed surface corresponding to the protruding surface is formed on an outer surface of the tire in the vent plug, the projection having the above shape is distinctive and thus there is a risk that the projection gives an outer appearance of the tire a feeling of strangeness.